How to use >3G memory per process

How to use >3G memory per process

[Wenyong Deng]

Hi,

I read about 3.5G-per_process (or 3.5G/0.5G user/kernel space) in this
mailing list, but I don't find the details of how to do it. I have installed
Redhat7.2 (kernel 2.4.10enterprise) on a dual CPU 4G memory PC. I wrote a
simple program to use malloc to allocate memory, and it can never exceeds
3G. libhoard didn't help either. My question is:

[1] What need to be done for the kernel to support 3.5G or more user address
space per process?

[2] What need to be done at compilation time? Any option for
compiler/linker?

Thanks,

--Wenyong

Re: How to use >3G memory per process

[Wayne Whitney]

In mailing-lists.linux-kernel, you wrote:

> [1] What need to be done for the kernel to support 3.5G or more user
> address space per process?

On ia32, change the value of __PAGE_OFFSET (where kernel space starts)
in include/asm-i386/page.h.  The size of kernel space must be a power
of 2, so you can change __PAGE_OFFSET from its default of 0xC0000000
to either 0xE0000000 (reasonable) or 0xF0000000 (overboard ?).
You must also change the unlabeled value near the top of
arch/i386/vmlinux.lds to match the value of __PAGE_OFFSET.

> [2] What need to be done at compilation time? Any option for
> compiler/linker?

No changes are required in the method of compiling the kernel.  As for
your application, no changes should be required, although I am not
familiar with libhoard.  

Note that this change increases the mmap() region of user space, but
since you are speak of using malloc() and/or libhoard, that should be
sufficient for your purposes.  With __PAGE_OFFSET set to 0xE0000000,
your program should have (3.5GB - 2 * Program Size - Stack Size) of
usable address space.

Cheers, Wayne

Re: How to use >3G memory per process

[H. Peter Anvin]

Followup to:  <200112181837.fBIIbUF02685@adsl-209-76-109-63.dsl.snfc21.pacbell.net>
By author:    Wayne Whitney <whitney@math.berkeley.edu>
In newsgroup: linux.dev.kernel
>
> In mailing-lists.linux-kernel, you wrote:
> 
> > [1] What need to be done for the kernel to support 3.5G or more user
> > address space per process?
> 
> On ia32, change the value of __PAGE_OFFSET (where kernel space starts)
> in include/asm-i386/page.h.  The size of kernel space must be a power
> of 2, so you can change __PAGE_OFFSET from its default of 0xC0000000
> to either 0xE0000000 (reasonable) or 0xF0000000 (overboard ?).
> You must also change the unlabeled value near the top of
> arch/i386/vmlinux.lds to match the value of __PAGE_OFFSET.
> 

Note that this does break the (old) initrd protocol.  Compile your
kernel monolithic.

	-hpa
-- 
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!
"Unix gives you enough rope to shoot yourself in the foot."
http://www.zytor.com/~hpa/puzzle.txt	<amsp@zytor.com>

Re: How to use >3G memory per process

[H. Peter Anvin]

Followup to:  <OHEPLPGMMIEGHANJIEBAIEPKCEAA.wydeng@platodesign.com>
By author:    "Wenyong Deng" <wydeng@platodesign.com>
In newsgroup: linux.dev.kernel
>
> Hi,
> 
> I read about 3.5G-per_process (or 3.5G/0.5G user/kernel space) in this
> mailing list, but I don't find the details of how to do it. I have installed
> Redhat7.2 (kernel 2.4.10enterprise) on a dual CPU 4G memory PC. I wrote a
> simple program to use malloc to allocate memory, and it can never exceeds
> 3G. libhoard didn't help either. My question is:
> 
> [1] What need to be done for the kernel to support 3.5G or more user address
> space per process?
> 
> [2] What need to be done at compilation time? Any option for
> compiler/linker?
> 

You need a patch from Andrea; you also need to either run kernel boot
protocol 2.03 (a patch from me, plus a compatible bootloader), *OR*
run without initrd.

	-hpa
-- 
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!
"Unix gives you enough rope to shoot yourself in the foot."
http://www.zytor.com/~hpa/puzzle.txt	<amsp@zytor.com>